Bat monitoring in the Eglinton Valley

Hannah Edmonds

By Hannah Edmonds, Biodiversity Ranger

The Eglinton Valley in Fiordland contains populations of both species of New Zealand’s native bat – long and short-tailed.

Every January a select band of DOC staff head to the Eglinton Valley in Fiordland to measure the populations of these rare species.

Eglinton Valley happens to be home to the only known population on the mainland South Island of the nationally endangered lesser short tailed bat.

Native bat

The DOC staff also run a ‘Birds, Bats and BBQs’ event in the Eglinton Valley throughout January. This offers the public a chance to get involved with ongoing bat monitoring work.

Modern monitoring uses a host of innovative techniques to build up an accurate picture of population size and health – which is where the ‘Birds, Bats and BBQs’ night comes in.

After a hearty BBQ, and on the approach of dusk, the bat team and volunteers set out on their mission to locate, catch and assess Fiordland’s bats.

Catching and assessing Fiordland’s bats

The first step is to find the bats. Roosts are located by following bats previously fitted with radio transmitters, or by checking known roost trees.

The team then captures the bats by setting up a mist-net and calling them in with a bird squeaker, imitating the sound of a bat ‘singing’.

Collecting data on the bats

Once a bat is caught it undergoes a health check and, if required, has a transmitter attached to its back between the shoulder blades with contact adhesive.

Transmitters are usually put on adult lactating female bats, as these are more likely to return to a maternal roost, whereas non-breeding females and males will more often use solitary roosts.

As an additional step, the team climbs roost trees to mount infrared cameras, in order to record the bats emerging. This helps to provide an estimate of roost population size.

Impressive wing

More accurate bat population monitoring is achieved through tagging. Transponders and microchips were pioneered for bat monitoring in the Eglinton Valley in 2006 and are very effective in observing population trends.

The tags used in lesser short-tailed bats are 12 mm long, 2 mm in diameter and are inserted under the skin.

At least three people are required to tag bats: a handler (to hold the bat), an injector (to insert the tag), and a recorder (to record the data and prepare needles). A Joker, Riddler and Penguin are optional extras!

Tagging a bat.

All bats captured are scanned using a purpose-built scanner. If the bat has been captured on a previous monitoring mission, the scanner will read and store its data and the bat can be released. If the bat is new, the bat is tagged, scanned and their details recorded.

The big release

Tagged bats can also be logged remotely via antennae fitted onto roost trees. As bats move in and out of the roost the reader registers their tag which the logger automatically records, along with the date and time.

Following wide scale pest operations, bat numbers in the Eglinton Valley appear to be increasing slowly. Because bats only give birth to single young once a year, recovery will be slow and difficult to detect in the short term, hence requiring a long-term commitment to population monitoring.

Short-tailed bat video

Share a moment with a baby short-tailed bat, before DOC rangers return it home.